How to be an invasive gammarid (Amphipoda: Gammaroidea)–comparison of life history traits

About six life history and two ecological traits of gammarid species occurring in Central European waters were compared in order to identify the characters of successful invader. The species were (1) natives: Gammarus fossarum, G. pulex, G. lacustris, G. varsoviensis, G. balcanicus, G. leopoliensis, G. roeselii, and (2) aliens: Gammarus tigrinus, Chaetogammarus ischnus (=Echinogammarus ischnus), Pontogammarus robustoides, Obesogammarus crassus, Dikerogammarus haemobaphes, D. villosus. Generally the alien species were characterised by a combination of large brood size, high partial fecundity, early maturation and by appearance of higher number of generations per year. Also, these species presented higher tolerance towards severe environmental conditions, i.e. elevated salinity and human degradation of the environment. The above features seem to facilitate the colonisation of new areas and competition with native species -- a phenomenon that has been currently observed in various parts of Europe.     

Reproductive biology of Dikerogammarus haemobaphes: an invasive gammarid (Crustacea: Amphipoda) colonizing running waters in Central Europe

Dikerogammarus haemobaphes is a Ponto-Caspian gammarid that has invaded vast areas in Central and Western Europe. Our paper is a first presentation of its life history features in an invaded region. The study was conducted in the Vistula River in Poland from autumn 2003 to autumn 2005 in two sites differing in hydrological conditions with one being water reservoir. The results showed that the reproductive period lasted 8 months from April till October in both sites. Three generations per 1 year were observed: autumn (overwintering), spring and summer. Ten cohorts per year were distinguished. The individuals from the reservoir were much bigger than those from the other site. The fecundity of those specimens was also higher and they laid 52 eggs per clutch in average in comparison with 37 eggs in the river itself. The strong relationship between the number of embryos (in developmental stage 2) per clutch and the length of females was noticed. The overall mean egg size of stage 2 of D. haemobaphes was 0.430 ± 0.029 mm which is smaller than noted for native species such as Gammarus fossarum. A potentially high reproductive capacity, comparatively small eggs, short time of eggs’ development, fast reaching sexual maturation, short life span, tolerance to a wide range of environmental conditions, all promote the invasion of this Ponto-Caspian gammarid in freshwater ecosystems of the temperate climate zone.     

Survival in northern microrefugia in an endemic Carpathian gammarid (Crustacea: Amphipoda)

Gammarus leopoliensis (Crustacea: Amphipoda) is considered a north‐eastern Carpathian endemic species and therefore can be regarded as an appropriate model for testing the hypothesis of Quaternary glacial survival in northern microrefugia. However, 250 km south, the south‐western Carpathians harbour populations that resemble phenotypically both G. leopoliensis and Gammarus kischineffensis, a similar species distributed east of the Carpathians. We used maximum‐likelihood and Bayesian methods to evaluate the phylogenetic relationships of these three taxa based on mitochondrial and nuclear markers, and quantitatively compared diversity patterns, phylogeography and divergence times among north‐eastern and south‐western Carpathian taxa. Results indicate that G. leopoliensis and the south‐western populations form together a strongly supported group (G. leopoliensis s.l.) which, along with G. kischineffensis, belongs to the Gammarus balcanicus clade. This group contains 12 lineages mainly of Pliocene age. G. leopoliensis consists of two widely distributed and recently expanded allopatric sister lineages that diverged from the southern ones ca. 4 Ma, indicating long‐term survival in northern microrefugia. The southern lineages are micro‐endemic and display a scattered distribution, suggesting a more ancient, relict pattern. We conclude that the contrasting diversity patterns between the disjunct distributional areas of G. leopoliensis s.l. reflect differential survival of lineages across the latitudinal gradient, offering a promising system for comparing the evolutionary ecology of lineages persisting in latitudinally disconnected microrefugia. These results fill an important gap in the knowledge of European gammarid biogeography and reveal that all Carpathian Gammarus taxa are ancient and diverse species complexes.     

Molecular markers for systematic identification and population genetics of the invasive Ponto‐Caspian freshwater gammarid Dikerogammarus villosus (Crustacea,Amphipoda)

The Ponto‐Caspian amphipod, Dikerogammarus villosus, is an invasive species of many European rivers. First, we show that size difference of nrDNA ITS1 allows discriminating D. villosus from Dikerogammarus bispinosus, a closely related but morphologically hardly distinguishable species. Second, we present two types of polymorphic markers for D. villosus, three microsatellites and two single nucleotide polymorphisms (SNPs) of mtDNA COI gene, which were scored by polymerase chain reaction‐single strand conformational polymorphism (PCR‐SSCP). These markers will be very useful in studying population genetics of D. villosus.     

Preferences of juveniles and adults of the invasive Ponto-Caspian amphipod <Emphasis Type="Italic">Pontogammarus robustoides</Emphasis> for various species of macrophytes and artificial substrata

We studied preferences of invasive Ponto-Caspian amphipod P. robustoides for various macrophyte species (Myriophyllum spicatum, Ceratophyllum demersum, Potamogeton perfoliatus, Elodea canadensis) and artificial plant-like objects (artificial Christmas tree branches) in laboratory pairwise-choice tests. Juvenile (<7 mm) and adult gammarids exhibited different habitat preferences. Adults did not discriminate between artificial and natural substrata, or among most of the tested species of plants. In contrast, juveniles clearly preferred all tested macrophytes over artificial substrata. Moreover, they particularly preferred plants with the finest leaf elements: M. spicatum and C. demersum over the others and E. canadensis over P. perfoliatus. We found no influence of chironomid larvae, a potential food source for adult gammarids, on their distribution, nor any effect of adults on the habitat choice by juveniles. The habitat partitioning between juvenile and adult P. robustoides may help them survive in a new environment and increase their invasive potential by reducing the intraspecific competition and cannibalism.     

Feeding preferences of an invasive Ponto‐Caspian goby for native and non‐native gammarid prey

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Feeding on micro-algae in the invasive Ponto-Caspian amphipod Dikerogammarus villosus (Sowinsky, 1894)

Feeding on micro-algae is shown in the invasive Ponto-Caspian amphipod Dikerogammarus villosus. Compared with controls, males, females and juveniles of this species significantly reduced the concentration in suspension of unicellular micro-algae. Juveniles had higher concentrations of algae in the cardiac gut than adults. The presence of these algae in the mid- and hindgut was also recorded. This feeding behaviour was filmed and the mechanisms involved are described and discussed. We comment on the use of the Functional Feeding Group (FFG) concept to classify feeding in amphipods. The role of being a feeding-generalist in aiding the invasion process is also discussed.An erratum to this article can be found at     

Niche differentiation among invasive Ponto-Caspian <Emphasis Type="Italic">Chelicorophium</Emphasis> species (Crustacea,Amphipoda, Corophiidae) by food particle size

After Chelicorophium curvispinum, two other Ponto-Caspian tube-dwelling, filter-feeding amphipod species (Chelicorophium robustum and Chelicorophium sowinskyi) have colonized several catchments in Central and Western Europe in recent decades. To reveal the mechanism of niche differentiation among them, we measured the mesh sizes of their filtering apparatus and analyzed multi-habitat sampling data from the River Danube using RDA-based variance partitioning between environmental and spatial explanatory variables. Morphometric data showed a clear differentiation among the species by filter mesh size (C. curvispinum?>?C. robustum?>?C. sowinskyi). Field data also indicated the relevance of suspended matter; however, the mere quantity of suspended solids included in the analysis could not explain the abundance patterns effectively. Current velocity, substrate types, and total nitrogen content also had a non-negligible effect; however, their role in the niche differentiation of the species is not evident. In summary, differences in their filter mesh sizes indicate a niche differentiation by food particle size among the invasive Chelicorophium species, allowing their stable coexistence given sufficient size variability in their food source. Consequently, the two recent invaders increase the effectiveness of resource utilization, resulting in a more intensive benthic–pelagic coupling in the colonized ecosystems.     

Strahlenbiologische Untersuchungen an Gammariden (Crustacea,Amphipoda)

Zusammenfassung 1. Der Einfluß einmaliger Röntgenbestrahlungen auf die Überlebenszeiten der euryhalinen AmphipodenGammarus duebeni Lilljeborg,Gammarus salinus Spooner undGammarus zaddachi Sexton wurde bei einer konstanten Temperatur von 15⁰ C und einem Salzgehalt von 10 untersucht.2. Bestrahlungen mit Dosen von 625 und 1250 R führen beiG. duebeni zum vorzeitigen Tod von nur einigen Versuchstieren, Bestrahlungen mit 2500 R und höheren Dosen zum vorzeitigen Tod aller Versuchstiere.3. BeiG. duebeni sind die strahlenempfindlicher als die , die Jungtiere strahlenempfindlicher als adulte Individuen.4.G. salinus undG. zaddachi sind strahlenempfindlicher alsG. duebeni.5. Die LD₅₀-Kurven lassen drei Bereiche erkennen. Bei mittleren Dosen ändert sich die Zeitspanne, in der 50% der Versuchstiere sterben, nur wenig oder gar nicht mit der Dosis. Bei hohen und niedrigen Dosen ist die Überlebenszeit dosisabhängig.6. Die Strahlenempfindlichkeit vonG. duebeni war im ersten Quartal des Jahres 1967, in dem die Temperaturen über den langfristigen Monatsmitteln lagen, geringer als bei Flohkrebsen, die zu einem späteren Zeitpunkt gefangen wurden oder aus Laboratoriumszuchten stammten.7. Die Häutungsvorgänge, deren Beeinflussung nur beiG. duebeni untersucht wurde, werden durch Bestrahlungen mit 1250 R oder geringeren Dosen nicht beeinflußt.8. Nach einer Bestrahlung mit 20 000 R sind 2 Tage nach der Bestrahlung nur wenige oder gar keine Häutungen möglich. Nach Bestrahlungen mit 10 000 und 5000 R erfolgen die Häutungen verspätet.9. Als Folge von Bestrahlungen mit letalen Dosen nimmt die Zahl der Häutungen um den 30. Tag nach der Bestrahlung ab.10. Die Häutungsvorgänge waren bei Tieren, die im ersten Quartal 1967 gefangen und bestrahlt wurden, weniger beeinflußbar als bei Tieren, die aus Laboratoriumszuchten stammten oder zu einem späteren Zeitpunkt gefangen wurden.11. Nach Bestrahlungen mit letalen Dosen treten zwei kritische Phasen auf. Ein Teil der mit mittleren und der größte Teil der mit hohen Dosen bestrahlten Tiere stirbt bereits in der ersten kritischen Phase. Die zweite kritische Phase wird von allen mit niedrigen Dosen bestrahlten Tieren erreicht. Tiere, die sich in der ersten kritischen Phase häuten, haben eine geringe Lebenserwartung.12. Die Überlebenszeit des einzelnen Individuums hängt außer von der Bestrahlungsdosis von dem Zeitpunkt ab, zu dem es sich innerhalb der Versuchszeit häutet.

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Radiobiological investigations on gammarids (Crustacea, Amphipoda)

Effects of single exposures of X-radiation on survival were studied inGammarus duebeni, G. salinus andG. zaddachi under constant conditions of temperature (15⁰ C) and salinity (10 ). Effects on moulting were investigated inG. duebeni. The amphipods were irradiated with doses between 625 and 20,000 R.G. salinus andG. zaddachi are equally radioresistant (LD_50/30 : 1,700 R) but less resistant thanG. duebeni (LD_50/30(males) : 3,900 R; LD_{50/30(females)} : 3,500 R). At high doses, half of the test individuals die within a few days; at medium doses survival time is dose-independent; at lower doses survival time again increases with decreasing doses up to dose-ranges (below 1,250 R forG. duebeni, 1,000 R forG. salinus andG. zaddachi), at which only a few individuals die before their natural death. Subadult gammarids are less resistant;G. duebeni of 4 to 7 mm body length have a LD_50/30 of 2,200 R. Death distribution after medium doses indicates that at least two mechanisms are involved in acute mortality. A first mortality maximum occurs shortly after irradiation; subsequently, mortality decreases for a few days, and is followed by another maximum. At lower doses no individual dies during the first critical period. Shortening of survival time at higher doses results from survival of fewer individuals to the second critical period. Few or no moults occur inG. duebeni irradiated with 20,000 R following the second day after irradiation and after the 30th day in those individuals irradiated with 2,500 to 10,000 R; moulting is delayed after exposure to 5,000 to 10,000 R. Individuals ofG. duebeni taken from the field during the mild winter 1966/67 were more resistant to radiation, and moulting was less affected, than in laboratory-reared amphipods, or in those collected in the field during other seasons. Besides on irradiation dose, survival time of an individual depends on the time of its moulting in the course of an experiment.

     

Recruitment preferences of blue mussel spat (Mytilus edulis) for different substrata and microhabitats in the White Sea (Russia)

We adapted the chloroform fumigation method to determine microbial nitrogen (N) and microbial incorporation of ¹⁵N on three common substrates [leaves, wood and fine benthic organic matter (FBOM)] in three forest streams. We compared microbial N and ¹⁵N content of samples collected during a 6-week ¹⁵N–NH₄ tracer addition in each stream. The ¹⁵N was added during late autumn to Upper Ball Creek, a second-order stream at the Coweeta Hydrologic Lab, North Carolina, U.S.A.; during spring to Walker Branch, a first-order stream on DOE's Oak Ridge National Environmental Research Park, Tennessee; and during summer to Bear Brook, a first-order stream in the Hubbard Brook Experimental Forest, New Hampshire. FBOM was the largest component of organic matter and N standing stock in all streams. Microbial N represented the highest proportion of total N in leaves and least in FBOM in Walker Branch and Bear Brook. In Upper Ball Creek, the proportion of microbial N was higher in FBOM than in used biofilm or on leaves. Standing stock of microbial N on leaves and in FBOM ranged from 37 mg N m^–2 in Bear Brook to 301 mg N m^–2 in Walker Branch. Percent of detrital N in living microbial cells was directly related to total microbial biomass (fungal and bacterial biomass) determined from microscopic counts. ¹⁵N values for microbes were generally higher than for bulk detritus, which would result in higher ¹⁵N values for animals preferentially consuming or assimilating microbial cells. The proportion of ¹⁵N taken up by detritus during the ¹⁵N experiments that remained in microbial cells by the end of the experiments was highest for wood biofilm in Upper Ball Creek (69%), leaves in Walker Branch (65%) and FBOM in Upper Ball Creek (31%). Lower retention proportions (<1–25%) were observed for other substrates. Our results suggest that microbial cells associated with leaves and wood biofilm were most active in ¹⁵N–NH₄ immobilization, whereas microbial cells associated with FBOM immobilized little ¹⁵N from stream water.     

Recent drastic changes in the gammarid fauna (Crustacea, Amphipoda) of the Vistula River deltaic system in Poland caused by alien invaders

During the last decade of 20th century, the nonindigenous gammarid species Gammarus tigrinus, Dikerogammarus haemobaphes, Pontogammarus robustoides and Obesogammarus crassus invaded the lower Vistula River and its deltaic, partly brackish regions. G. tigrinus, an oligohaline North‐American species, was introduced to western Europe in the 1950s; the remaining three species are oligohaline/freshwater Ponto‐Caspian species. All these species are now invading central and western Europe using the network of man‐made canals connecting different European river systems. In the Vistula River, the native European freshwater gammarid species Gammarus pulex and G. varsoviensis were replaced in the 1920s by the Ponto‐Caspian Chaetogammarus ischnus (syn. Echinogammarus ischnus), which in turn has been outnumbered by the more recent invasions of D. haemobaphes and P. robustoides. In brackish waters, the native Atlantic‐boreal species Gammarus zaddachi and Gammarus duebeni are replaced or at least outnumbered by G. tigrinus, P. robustoides and O. crassus. Possible invasion routes are discussed.     

Complete mitochondrial genome sequence of the Arctic gammarid,Onisimus nanseni (Crustacea; Amphipoda): Novel gene structures and unusual control region features

To analyze the mitogenome of the amphipod Onisimus nanseni, we amplified the complete mitogenome of O. nanseni using long-PCR and genome walking techniques. The mitogenome of O. nanseni is circular and contains all the typical mt genes (2 rRNAs, 22 tRNAs, and 13 protein-coding genes). It has two peculiar non-coding regions of 148 bp and 194 bp. The latter can be involved in replication and termination processes. The total length of the pooled protein-coding, rRNA, and tRNA genes is shorter than those of other crustaceans. In addition, the intergenic spacers of the O. nanseni mitogenome are considerably shorter in length than those of other crustaceans. Fourteen adjacent genes overlap, resulting in a compact mitogenomic structure. In the O. nanseni mitogenome, the AT composition is elevated, particularly in the control regions (78.9% AT), as has been demonstrated for two other amphipods. The tRNA order is highly rearranged compared to other arthropod mitogenomes, but the order of protein-coding genes and rRNAs is largely conserved. The gene cluster between the CO1 and CO3 genes is completely conserved among all amphipods compared. This provides insights into the evolution and gene structures of crustacean mitochondrial genomes, particularly in amphipods.     

Experimental studies on the life cycle ofJassa falcata (Crustacea,Amphipoda)

Jassa falcata (Leach), an unselective suspension feeder, was cultivated in standing, unaerated finger bowls, feeding on a mixture ofBrachionus plicatilis, Scrippsiella faeroense, Ulva spec., and natural detritus. This amphipod can also be maintained with diets composed of dead or live material of both plant and animal origin, but an addition of living zooplankton is necessary for longterm cultivation. Starvation resistance is higher in females than in males, and it is increased by lower temperatures. The life span ofJ. falcata increases with decreasing temperature, and it is generally higher in females (maximum: 252 days at 10°C) than in males. In laboratory culture, a bimodal mortality pattern is typical with high juvenile death rates, low mortality during the reproductive phase, and again increasingly high death rates toward the end of the life cycle. Growth rate depends on temperature, sex, and individual age. The temperature dependence of growth is particularly high in males, and it is higher in adults than in juveniles. The total number of moults is lower in males (5 to 6) than in females (7 to 9). Sexual maturity is attained at moult IV to V. The average incubation time of eggs is about 9 to 16 days (highest value at 10°C). Three to 4 broods were observed, with largest numbers of offspring at 10°C.     

Allee effect in an invasive alien plant, pale swallow-wort Vincetoxicum rossicum (Asclepiadaceae)

I tested for the presence of an Allee effect in pale swallow-wort Vincetoxicum rossicum , an invasive alien vine, by planting 1-, 9- and 81-plant patches in an old field. Biomass and seed set of central "target" plants were significantly higher in the 81-plant patches than in the 1- and 9-plant patches. Biomass of roots did not differ significantly among treatments. The nine central plants of the 81-plant patches also had higher biomass and produced more seeds than the nine plants of the 9-plant treatment. Unlike most other examples of Allee effects in plants, the effect in V. rossicum was not due to differences in pollinator visitation rates. Instead, V. rossicum appears to suppress background vegetation more effectively when growing in larger patches. Like many other invasives, V. rossicum has been present in North America for years before it attained pest status. The Allee effect is one of several mechanisms that may contribute to such a latency period.     

Benthic diatoms of the Vistula River estuary (Northern Poland): Seasonality,substrata preferences,and the influence of water chemistry

Seasonal studies of water bodies in separate branches of the Vistula River estuary in Northern Poland were conducted over 30 months from May 2005 to October 2007. Diatom samples were collected from different substrata from two sites located in the river mouth, which has physical characteristics as a result of a complex interplay of natural and human influences that have taken place over the last 100+ years. The diatom flora growing on hard surfaces near the river banks such as sand, muddy sand, rocks, macroscopic green algae and/or vascular aquatic plants was recorded. All diatom taxa collected were distinguished based on their morphological features using light (LM) and scanning electron microscopy (SEM). A total of 187 species belonging to 61 genera were identified. A canonical correspondence analysis indicated that the diatom assemblages were definitely associated with salinity as well as nutrient concentrations and substratum type. During the study, malformations of diatom valves were observed in 48% of the microphytobenthos samples. Abnormal outline morphology and ornamentation deformities in several individuals of nine different species were recorded, which were mainly in epilithic and epiphytic communities collected from spring to autumn.     

Spatio-temporal analysis of an invasive plant pathogen (Phytophthora ramorum) in England and Wales

Phytophthora ramorum is a damaging invasive plant pathogen and was first discovered in the UK in 2002. Spatial point analyses were applied to the occurrence of this disease in England and Wales during the period of 2003–2006 in order to assess its spatio-temporal spread. Out of the 4301 garden centres and nurseries (GCN) surveyed, there were 164, 105, 123 and 41 sites with P. ramorum in 2003, 2004, 2005 and 2006, respectively. Spatial analysis of the observed point patterns of GCN outbreaks suggested that these sites were significantly clumped within a radius of ca 60 km in 2003, but not in later years. Further analyses were conducted to determine the relationship of GCN outbreak sites over two consecutive years and thus to infer possible disease spread over time. This analysis suggested that disease spread among GCN sites was most likely to have occurred within a distance of 60 km for 2003–2004, but not for the later years. There were 35, 63, 81 and 58 sites with P. ramorum in the semi-natural environment (SNE). Analyses were carried out to assess whether infected GCN sites could act as an inoculum source of infected SNE plants or vice versa. In all years, there was a significant spatial closeness among GCN and SNE outbreak sites within a distance of 1 km. But a significant relationship over a longer distance (within 60 km) was only observed between cases in 2003 and 2004. These analyses suggest that statutory actions taken so far appear to have reduced the extent of long-distance spread of P. ramorum among garden centres and nurseries, but not the disease spread at a shorter distance between GCN and SNE sites.     

Contrasting effects of an invasive ant on a native and an invasive plant

When invasive species establish in new environments, they may disrupt existing or create new interactions with resident species. Understanding of the functioning of invaded ecosystems will benefit from careful investigation of resulting species-level interactions. We manipulated ant visitation to compare how invasive ant mutualisms affect two common plants, one native and one invasive, on a sub-tropical Indian Ocean island. Technomyrmex albipes, an introduced species, was the most common and abundant ant visitor to the plants. T. albipes were attracted to extrafloral nectaries on the invasive tree (Leucaena leucocephala) and deterred the plant’s primary herbivore, the Leucaena psyllid (Heteropsylla cubana). Ant exclusion from L. leucocephala resulted in decreased plant growth and seed production by 22% and 35%, respectively. In contrast, on the native shrub (Scaevola taccada), T. albipes frequently tended sap-sucking hemipterans, and ant exclusion resulted in 30% and 23% increases in growth and fruit production, respectively. Stable isotope analysis confirmed the more predacious and herbivorous diets of T. albipes on the invasive and native plants, respectively. Thus the ants’ interactions protect the invasive plant from its main herbivore while also exacerbating the effects of herbivores on the native plant. Ultimately, the negative effects on the native plant and positive effects on the invasive plant may work in concert to facilitate invasion by the invasive plant. Our findings underscore the importance of investigating facilitative interactions in a community context and the multiple and diverse interactions shaping novel ecosystems.     

Interactions between density-dependent processes, population dynamics and control of an invasive plant species, Tripleurospermum perforatum (scentless chamomile)

Tripleurospermum perforatum is an invasive weedy species which exhibits strong over-compensating density dependence. Interactions between density-dependent survival, probability of flowering and fecundity were modelled and their impact on the population dynamics were examined. When only fecundity was density-dependent, the dynamics were similar to those observed in the model containing all three density-dependent terms. Density-dependent survival was a stabilizing process when acting in combination with density-dependent fecundity and probability of flowering; removing density-dependent survival from the model produced two-point cycles. The addition of a seed bank was also stabilizing. Simulations of control strategies at different life-history stages indicated that full control would be difficult due to the strong over-compensating density dependence, with severe reductions in fecundity and late season survival necessary in order to reduce equilibrium seed density and biomass.